Immunocytochemical localization of gonadotropin-releasing hormone (Gn-RH) and neuropeptides implicated to be modulating substances for release of Gn-RH will be visualized in the hypothalamus and median eminence of rats and mice. Initial studies are intended to establish consistent and specific staining for Gn-RH using the pre-embedding immunocytochemical method. Specificity of the reaction will be determined by immunoabsorption of antisera to Gn-RH neurons and their processes will be determined in serial-sectioned rat brains. The subcellular localization for Gn-RH neurons during states of synthesis and secretion will be studied before and after the administration of prostaglandin E2. The extrahypothalamic innervation of Gn-RH projections to various brain areas will be determined; and receptors for Gn-RH on target neurons will be confirmed using ultrastructural autoradiography after the intraventricular injection of monoiodinated Gn-RH. Finally, double-staining immunocytochemical techniques for the simultaneous demonstration of two antigens on the same section will be developed for the ultrastructural visualization of dopamine-B-hydroxylase and Gn-RH, as well as for vasopressin and Gn-RH so that synaptic interrelationships can be established for noradrenergic and vasopressinergic terminals on Gn-RH cells and fibers.